Process of preparing continuous filament composed of nano fiber

ABSTRACT

The present invention relates to a process of preparing a continuous filament composed of a nano fiber, wherein nano fibers are prepared by spinning a polymer spinning dope in a spinning dope main tank ( 20 ) onto the surface of water or organic solvent ( 4   a ) of a collector ( 4 ), which contains water or inorganic solvent ( 4   a ) and has a conductive material ( 5 ) with a high voltage applied sunken in the water or organic solvent ( 4   a ), through nozzles ( 2 ) with a high voltage applied, and the nano fibers are pressed, drawn, dried and wound while being pulled by a rotary roller ( 6 ) rotating at a constant linear velocity from the location spaced more than 1 cm from one end of a dropping spot. The present invention can prepare a continuous filament composed of a nano fiber by an electrospinning method and a continuous process.

TECHNICAL FIELD

The present invention relates to a process of preparing a continuousfilament or yarn (hereinafter, commonly referred to as a “filament”)composed of nano fibers, and more particularly, to a process ofpreparing a continuous filament composed of nano fibers, using anelectrospinning method.

In the present invention, the nano fiber defines a fiber having a fiberdiameter of less than 1,000 nm, more preferably, less than 500 nm.

A woven fabric composed of nano fibers can be utilized for makingartificial leather, filters, diapers, sanitary pads, sutures,antisetting agents, wiping cloth, artificial vessels, bone fixingdevices and the like, and is particularly useful for the production ofthe artificial leather.

BACKGROUND ART

As conventional techniques for preparing an ultra fine fiber or nanofiber suitable for the production of an artificial leather, there areknown a sea-island type conjugated spinning method, a split typeconjugated spinning method, a blend spinning method and the likeHowever, in case of the sea-island type conjugated spinning method orthe blend spinning method, one of two polymer components consisting of afiber must be dissolved and removed to make the ultra fine fiber. Inorder to produce artificial leather from fiber prepared by thesemethods, a complex process must be carried out, including melt spinning,fiber production, non-woven fabric production, urethane impregnation andsingle component dissolution.

Nevertheless, it is impossible to produce a fiber with a diameter ofless than 1,000 nm by the above two methods.

In case of the spit type conjugate spinning method, it is problematic inthat since two polymer components (for example, a polyester and apolyamide) with different dyeing properties co-exist in the fiber,uneven dyeing is exhibited and the artificial leather production processis complicated. In addition, it is difficult to produce a fiber with adiameter less than 2,000 nm by the above method.

Another conventional technique for preparing nano fibers is theelectrospinning method. In the electrospinning method, as shown in FIG.4, a polymer spinning dope in a spinning dope main tank (20) iscontinuously and constantly fed to a plurality of nozzles (2), to whicha high voltage is applied, through a metering pump (21). Subsequently,the spinning dope fed to the nozzles (2) is spun and collected throughthe nozzles (2) on a collector (4) of an endless belt type having a highvoltage of more than 5 kV, thereby producing a fiber web. The fiber webproduced is needle-punched in the next process to produce a non-wovenfabric composed of nano fibers.

As seen from above, the conventional electrospinning method can produceonly a web or non-woven fabric composed of a nano fiber less than 1,000nm. Hence, to prepare a continuous filament by the conventionalelectrospinning method, the produced nano fiber web has to be cut to apredetermined length to produce a staple and this staple has to undergoan additional spinning process to produce spun yarn, which makes theprocess complicated.

In case of the non-woven fabric composed of nano fiber, there is alimitation to employing the non-woven fabric to various fields ofapplication, such as the artificial leather, due to the limits in thephysical properties of the non-woven fabric. For reference, it isdifficult to achieve physical properties of more than 10 MPa fromnon-woven fabric composed of nano fiber.

The present invention is intended to prepare a continuous filamentcomposed of nano fiber utilizing a simple procedure of providing aprocess of continuously preparing a filament (yarn) using electricallyspun nano fiber web, without any additional spinning process.Additionally, the present invention is intended to provide a continuousfilament of nano fiber which is superior in physical properties and issuitable for various industrial materials, such as filters, diapers,sanitary pads, artificial vessels and so on, as well as artificialleather.

DISCLOSURE OF INVENTION

The present invention has been developed for the purpose of solving theforegoing problems and thus it is an object of the present invention toprovide a process of preparing a continuous filament composed of nanofiber, wherein nano fibers are prepared by spinning a polymer spinningdope in a spinning dope main tank (20) onto the surface of water or anorganic solvent (4 a) disposed in a collector (4), providing aconductive material (5) with a high voltage applied sunken in the wateror organic solvent (4 a), through nozzles (2) with a high voltageapplied, and the nano fibers are pressed, drawn, dried and wound whilebeing pulled by a rotary roller (6) rotating at a constant linearvelocity from the location spaced more than 1 cm from one end of adropping spot.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in detail with reference to theaccompanying drawings, now wherein,

FIG. 1 is a schematic view showing the process of the present invention;

FIG. 2 is an enlarged view of a collector used in the present invention;

FIG. 3 is a schematic view showing a process of spinning two kinds ofpolymer spinning dopes onto one collector;

FIG. 4 is a schematic view showing a process of a conventionalelectrospinning method for preparing a nano fiber web;

FIG. 5 is a scanning electron micrograph of a surface of an undrawnfilament (aggregate of nano fibers) prepared according to Example 1; and

FIG. 6 is a scanning electron micrograph of a surface of an undrawnfilament (aggregate of nano fibers) prepared according to Example 5.

DETAILED DESCRIPTION OF THE INVENTION

In the present invention, as shown in FIG. 1, a polymer spinning dopedisposed in a spinning dope main tank (20) is continuously fed to aplurality of nozzles (2) through a metering pump (21). The nozzles (2)have a high voltage of more than 5 kV applied therefor by a voltagegenerator (1).

Next, the constantly fed polymer spinning dope fed through the pluralityof nozzles (2) is electrically spun into spun nano fibers 3 onto thesurface of water or an organic solvent (4 a) in a collector (4)specifically provided to collect nano fiber.

The collector (4) is a container containing water or organic solvent (4a) and has a construction whereby a conductive material (5) having ahigh voltage of more than 5 kV applied thereto by the voltage generator(1) is submerged in the water or organic solvent (4 a) disposed in thecontainer.

The conductive material (5) is a metal plate or metal powder. Thedistance (h) from the surface of the water or organic solvent (4 a)contained in the collector (4) to the top surface of the conductivematerial (5) is 0.01 to 200 mm, more preferably, 5 to 50 mm.

If the distance (h) is too small, the spun nano fiber is placed indirect contact with the surface of the conductive material (5) andthereafter cannot be pulled away well by a rotary roller (6), therebymaking the process difficult. If the distance (h) is too large, thevoltage applied to the conductive material (5) is not transferred wellto the surface of water or organic solvent, thereby making the collectedstate of the nano fiber very poor.

The diameter of the spun nano fiber is less than 1,000 nm, morepreferably, less than 500 nm.

Next, the nano fibers, spun and collected on the surface of the water ororganic solvent (4 a) contained in the collector (4) are continuouslypulled by the rotary roller (6) to thus form an undrawn filament (anaggregate of nano fibers).

The angle (θ) between the nano fibers spun and collected on the surfaceof water or organic solvent (4 a) in the collector (4) and the undrawnfilament (aggregate of nano fibers) pulled by the rotary roller (6) is 0to 180° C., more preferably, 10 to 90° C.

The distance (d) from one end of the dropping spot of the nano fibers,to the initial point where the nano fibers are pulled by the rotaryroller (6) is more than 1 cm. If the distance (d) is less than 1 cm, thespun nano fibers are pulled up in a state where they have notsufficiently coagulated, thereby making the production of a continuousfilament more difficult.

Next, the undrawn filament (aggregate of nano fibers) pulled by therotary roller (6) to tension controlled 7 is pressed by press rollers(8), (9), (10) and (12) to remove the residual water or organic solventin the aggregate, then dried by drier (11) after being drawn betweendrawing rollers (8, 10 and 12) and then are wound by a winding roller(13). The drawn filament may be twisted by a twister before it is wound.

In the present invention, an electric spinning process, a process ofpulling nano fibers, a pressing process, a drawing process and a dryingprocess are continuously carried out.

The polymer spinning dope of the present invention is composed of apolyester resin, nylon resin, a polysulfon resin, a polylactic acid, acopolymer thereof or a mixture thereof.

As shown in FIG. 3, the present invention also includes a method ofpreparing a filament composed of a hybrid nano fiber by spinning morethan two kinds of polymer spinning dope to the surface of water ororganic solvent (4 a) contained in the same collector (4) through eachof the nozzles (2).

Additionally, the present invention also includes a method of preparinga filament composed of hybrid nano fibers by spinning two kinds ofpolymer spinning dope with respective nozzles (2) and a respectivecollector (4) and then blending the two kinds of spun nano fibers bypulling them with the same rotary roller (6).

Additionally, the present invention also includes a method of preparinga filament composed of hybrid nano fibers by twisting two kinds offilaments separately spun, drawn and wound according to the method ofthe present invention.

FIG. 1 is a schematic view showing the process of the present invention;

FIG. 2 is an enlarged view of a collector used in the present invention;

FIG. 3 is a schematic view showing a process of spinning two kinds ofpolymer spinning dopes onto one collector;

FIG. 4 is a schematic view showing a process of a conventionalelectrospinning method for preparing a nano fiber web;

FIG. 5 is a scanning electron micrograph of a surface of an undrawnfilament (aggregate of nano fibers) prepared according to Example 1; and

FIG. 6 is a scanning electron micrograph of a surface of an undrawnfilament (aggregate of nano fibers) prepared according to Example 5.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail withreference to examples. But, this invention is not limited to thefollowing examples.

Example 1

A polymer spinning dope was prepared by dissolving apoly(ε-caprolactone) polymer (purchased from Aldrich Chemical Company)having a number average molecular weight of 80,000 in a mixed solvent ofmethylene chloride/N, N′-dimethyl form amide (volume ratio: 75/25) at aconcentration of 13% by weight. The polymer spinning dope had a surfacetension of 35 mN/m, a solution viscosity of 35 centipoise at an ambienttemperature, an electric conductivity of 0.02 mS/m and a permittivityconstant of 90. The polymer spinning dope was constantly fed to 15nozzles (2) with a 1 mm diameter and a 25 kV voltage applied through ametering pump (21). Then, as shown in FIG. 1, the polymer spinning dopewas electrically spun onto a collector (4) of this invention, whichcontains water (4 a) and has a conductive material (5) of a copper platewith a 25 kV voltage and a 10 mm thickness sunken in the water (4 a),more concretely, onto the surface of water contained in the collector(4). The distance (h) from the surface of water to the top surface ofthe conductive material (5) was 1 cm. Continually, nano fibers spun andagglomerated on the surface of water contained in the container (4) werepulled by a rotary roller (6) with a linear velocity of 36 m/min to thusprepare an undrawn filament (aggregate of nano fibers). The angle(.theta.) between the nano fibers located on the water surface and theundrawn filament (aggregate of nano fibers) pulled by the rotary roller(6) was 30°. The distance (d) from one end of a dropping spot of thenano fibers to the initial point where the nano fibers are pulled by therotary roller (6) was 5 cm. The thusly prepared undrawn filament(aggregate of nano fibers) had a fineness of 108 deniers, a strength of0.22 g/d and an elongation of 106%, and an electron micrograph of thesurface thereof is as shown in FIG. 5. Continually, the undrawn filament(aggregate of nano fibers) having passed through the rotary roller waspressed by a press roller (9), dried by a drier (11) while being drawnby drawing rollers (8, 10 and 12) so that the total draw ratio becomes1.4 and then wound by a winding roller (13), thereby preparing acontinuous filament composed of a nano fiber. The finally preparedcontinuous filament (composed of a nano fiber and drawn) had a strengthof 1.4 g/d and an elongation of 35%.

Example 2

A polymer spinning dope was prepared by dissolving a nylon-6 resin,which has a relative viscosity of 3.2 in a 96% sulfuric acid solution,in a form acid at a concentration of 15% by weight. The polymer spinningdope had a surface tension of 49 mN/m, a solution viscosity of 40centipoise at an ambient temperature and an electric conductivity of 420mS/m. The polymer spinning dope was constantly fed to 15 nozzles (2)with a 1 mm diameter and a 30 kV voltage applied through a metering pump(21). Then, as shown in FIG. 1, the polymer spinning dope waselectrically spun onto a collector (4) of this invention, which containswater (4 a) and having a conductive material (5) of a copper plate witha 30 kV voltage and a 20 mm thickness sunken in the water (4 a), moreconcretely, onto the surface of water contained in the collector (4).The distance (h) from the surface of water to the top surface of theconductive material (5) was 1 cm. Continually, nano fibers spun andagglomerated on the surface of water were pulled by a rotary roller (6)with a linear velocity of 30 m/min to thus prepare an undrawn filament(aggregate of nano fibers). The angle (θ) between the nano fiberslocated on the water surface and the undrawn filament (aggregate of nanofibers) pulled by the rotary roller (6) was 40°. The distance (d) fromone end of a dropping spot of the nano fibers to the initial point wherethe nano fibers are pulled by the rotary roller (6) was 8 cm. Theprepared undrawn filament (aggregate of nano fibers) had a fineness of110 deniers, a strength of 0.56 g/d and an elongation of 205%.Continually, the undrawn filament (aggregate of nano fibers) havingpassed through the rotary roller was pressed by a press roller (9),dried by a drier (11) while being drawn by drawing rollers (8, 10 and12) so that the total draw ratio becomes 2.8 and then wound by a windingroller (13), thereby preparing a continuous filament composed of a nanofiber. The finally prepared continuous filament (composed of a nanofiber and drawn) had a strength of 2.8 g/d and an elongation of 35%.

Example 3

A polyester spinning dope (hereinafter, referred to as a spinning dopeB) was prepared by dissolving a polyester resin with an intrinsicviscosity of 0.64 in a mixed solvent of trifluoro acetic acid/methylenechloride (volume ratio: 50/50) at a concentration of 15% by weight. Thenylon-6 spinning dope (hereinafter, referred to as a “spinning dope A”)of Example 2 and the spinning dope B were constantly fed to 15 nozzles(2) with a 1 mm diameter and a 25 kV voltage applied alternately througha metering pump (21). Then, as shown in FIG. 1, the spinning dope A andthe spinning dope B were electrically spun onto a collector (4) of thisinvention, which contains water (4 a) and has a conductive material (5)of a copper plate with a 25 kV voltage and a 10 mm thickness sunken inthe water (4 a), more concretely, onto the surface of water contained inthe collector (4). The distance (h) from the surface of water to the topsurface of the conductive material (5) was 1 cm. Continually, nanofibers spun and agglomerated on the surface of water were pulled by arotary roller (6) with a linear velocity of 20 m/min to thus prepare ahybrid undrawn filament (aggregate of nano fibers). The angle (θ)between the nano fibers located on the water surface and the hybridundrawn filament (aggregate of nano fibers) pulled by the rotary roller(6) was 30°. The distance (d) from one end of a dropping spot of thenano fibers to the initial point where the nano fibers are pulled by therotary roller (6) was 5 cm. Continually, the undrawn filament (aggregateof nano fibers) having passed through the rotary roller was pressed by apress roller (9), dried by a drier (11) while being drawn by drawingrollers (8, 10 and 12) so that the total draw ratio becomes 3.0 and thenwound by a winding roller (13), thereby preparing a continuous filamentcomposed of a hybrid nano fiber. The finally prepared continuousfilament (composed of a nano fiber and drawn) had a strength of 2.7 g/dand an elongation of 46%.

Example 4

A polymer spinning dope was prepared by dissolving a polyvinyl alcohol(purchased from Celanese) having a number average molecular weight of65,000 and a viscosity of 96% in a 80° C. distilled water at aconcentration of 10% by weight and adding phosphoric acid therein sothat the polyvinyl alcohol has a pH 2.5. The polymer spinning dope wasconstantly fed to 15 nozzles (2) with a 1 mm diameter and a 20 kVvoltage applied through a metering pump (21). Then, as shown in FIG. 1,the polymer spinning dope was electrically spun onto a collector (4) ofthis invention, which contains ethanol (4 a) and having a conductivematerial (5) of a copper plate with a 20 kV voltage and a 20 mmthickness sunken in the ethanol (4 a), more concretely, onto the surfaceof ethanol contained in the collector (4). The distance (h) from thesurface of ethanol to the top surface of the conductive material (5) was1 cm. Continually, nano fibers spun and agglomerated on the surface ofethanol were pulled by a rotary roller (6) with a linear velocity of 30m/min to thus prepare an undrawn filament (aggregate of nano fibers).The angle (θ) between the nano fibers located on the ethanol surface andthe undrawn filament (aggregate of nano fibers) pulled by the rotaryroller (6) was 30°. The distance (d) from one end of a dropping spot ofthe nano fibers to the initial point where the nano fibers are pulled bythe rotary roller (6) was 10 cm. Continually, the undrawn filament(aggregate of nano fibers) having passed through the rotary roller waspressed by a press roller (9), dried by a drier (11) while being drawnby drawing rollers (8, 10 and 12) so that the total draw ratio becomes2.0 and then wound by a winding roller (13), thereby preparing acontinuous filament composed of a nano fiber. The finally preparedcontinuous filament (composed of a nano fiber and drawn) had a strengthof 1.5 g/d and an elongation of 45%. The average diameter of the nanofiber was 250 nm.

Example 5

A polymer spinning dope was prepared by dissolving a polyurethane resinhaving a molecular weight of 80,000 in a mixed solvent of dimethylformamide/tetrahydrofuran (volume ratio: 5/5) at a concentration of13.5% by weight. The polymer spinning dope was constantly fed to 15nozzles (2) with a 1 mm diameter and a 30 kV voltage applied through ametering pump (21). Then, as shown in FIG. 1, the polymer spinning dopewas electrically spun onto a collector (4) of this invention, whichcontains water (4 a) and having a conductive material (5) of a copperplate with a 30 kV voltage and a 10 mm thickness sunken in the water (4a), more concretely, onto the surface of water contained in thecollector (4). The distance (h) from the surface of water to the topsurface of the conductive material (5) was 1.5 cm. Continually, nanofibers spun and agglomerated on the surface of water were pulled by arotary roller (6) with a linear velocity of 36 m/min to thus prepare anundrawn filament (aggregate of nano fibers). The angle (θ) between thenano fibers located on the water surface and the undrawn filament(aggregate of nano fibers) pulled by the rotary roller (6) was 30°. Thedistance (d) from one end of a dropping spot of the nano fibers to theinitial point where the nano fibers are pulled by the rotary roller (6)was 10 cm. The thusly prepared undrawn filament (aggregate of nanofibers) had a fineness of 63.5 deniers, a strength of 0.5 g/d and anelongation of 106%, and an electron micrograph of the surface thereof isas shown in FIG. 6. Continually, the undrawn filament (aggregate of nanofibers) having passed through the rotary roller was pressed by a pressroller (9), dried by a drier (11) while being drawn by drawing rollers(8, 10 and 12) so that the total draw ratio becomes 1.4 and then woundby a winding roller (13), thereby preparing a continuous filamentcomposed of a nano fiber. The finally prepared continuous filament(composed of a nano fiber and drawn) had a strength of 1.2 g/d and anelongation of 80%.

INDUSTRIAL APPLICABILITY

The present invention produces a continuous filament composed of a nanofibers by a simpler, continuous procedure. The continuous filamentprepared according to the present invention is greatly improved inphysical properties and thus is useful in various industrial fields,such as an artificial dialyzing filter, artificial vessel, anti-adhesionagent, artificial bone and so on, as well as daily necessaries, such asartificial leather, air cleaning filters, wiping cloth, golf glove, wigand so on.

The invention claimed is:
 1. A process of preparing a continuousfilament composed of nano fibers, which comprises spinning a polymerspinning dope through nozzles onto a collector surface of water or anorganic solvent and which has a conductive material disposed below thecollector surface of said water or organic solvent, applying a highvoltage to said nozzles and said conductive material, and the nanofibers spun onto the surface of said water or organic solvent arepressed, drawn, dried and wound while being pulled by a rotary rollerrotating at a constant linear velocity at a location spaced more than 1cm from one end of a dropping spot where the spun polymer contacts thecollector surface.
 2. The process of claim 1, wherein the conductivematerial is a metal plate or a metal powder.
 3. The process of claim 1,wherein the distance from the surface of the water or organic solvent tothe top surface of the conductive material is 0.01 to 200 mm.
 4. Theprocess of claim 1, wherein the distance from the surface of the wateror organic solvent to the top surface of the conductive material is 5 to50 mm.
 5. The process of claim 1, wherein the angel (θ) between the nanofibers collected on the surface of the water or organic solvent and theundrawn filament (aggregate of nano fibers) pulled by a rotary roller is0 to 180°.
 6. The process of claim 1, wherein the angle (θ) between thenano fibers collected on the surface of the water or organic solvent andthe undrawn filament (aggregated of nano fibers) pulled by a rotary is10 to 90°.
 7. The process of claim 1, wherein the drawn filament (yarn)is twisted before being wound.
 8. The process of claim 1, wherein thediameter of the nano fibers is less than 1,000 nm.
 9. The process ofclaim 1, wherein the polymer spinning dope is selected from the groupconsisting of polyester resins, nylon resins, polysulfon resins, polylactic acid and a copolymer thereof or a mixture thereof.
 10. Theprocess of claim 1, wherein more than two kinds of polymer spinning dopeare spun onto the surface of the water or organic solvent to form twokinds of nano fibers, said two kinds of nano fibers being combinedtogether.